The in-Vivo Effects of Sheep Pituitary Gonadotrophins on the Secretion of Steroids by the Autotransplanted Ovary of the Ewe

Abstract

The transplanted ovary preparation in the ewe permits long-term access to both the arterial and venous sides of the ovarian circulation in the unstressed, unanaesthetized animal. However, these animals are not completely normal, as the separation of the ovary from the uterus results in ovarian cycles with a prolonged luteal phase and the infrequent manifestation of behavioural oestrus. Treatment with exogenous gonadotrophins made it possible to carry out direct infusion experiments on the transplanted ovary on a more uniform basis. The effect on ovarian blood flow and on ovarian steroid secretion following the infusion of ovine luteinizing hormone (LH), ovine follicle-stimulating hormone (FSH) or ovine prolactin directly into the arterial supply of the transplanted ovary of the ewe is described. Four infusions of each of the three ovine pituitary gonadotrophins were made into the ovary at rates varying from 0\m=.\1 \g=m\g./hr. to 1000 \g=m\g./hr. LH infusions produced an increase in both ovarian blood flow and steroid secretion at all dosage levels employed. Androstenedione showed the greatest increase (600%) in secretion rate after LH, followed by testosterone (400%), oestradiol (more than 50%) and progesterone (less than 50%). Progesterone however showed the greatest increase in terms of mass of steroid secreted. There was no measurable change in the secretion of oestrone. Ovarian blood flow increased by at least 20 % (range 20-125 %) within 1 hr. of beginning the LH infusion. On the other hand FSH and prolactin infused at the same or at a higher rate than LH, had essentially no effect on ovarian blood flow or steroid secretion rate. In two out of four FSH infusions there appeared to be a transient fall in progesterone secretion rate. The infusion of 0-9% NaCl solution into the ovary as a control had no effect on blood flow or on steroid secretion.

Relationship between LH receptor concentrations in thecal and granulosa cells and in-vivo and in-vitro steroid secretion by ovine follicles during the preovulatory period

“…LH, but not FSH, stimulates oestradiol secretion following infusion (McCracken, Uno, Goding, Ichikawa & Baird, 1969), and an endogenous pulse of LH has been associated with an increase in circulating oestradiol concentrations (Baird, Swanston & Scaramuzzi, 1976;Baird, 1978;Baird, Swanston & McNeilly, 1981). Paradoxically, the administration of high doses of LH in the sheep inhibits oestradiol secretion both in vivo and in vitro (Rado, McCracken & Baird, 1970;Moor, 1974) and elicits a similar response in the rat (Hori, Ide & Miyake, 1969;Hori, Ide, Kato & Miyake, 1970).…”

Neuroendocrine Regulation of the Estrous Cycle and Seasonal Breeding in the Ewe

“…tonic LH secretion is either a necessary or a sufficient stimulus for the preovulatory estradiol rise. It has been demonstrated, however, that ovarian secretion of estradiol in the ewe can be enhanced by the administration of LH (McCracken et al, 1969). Further, administration of human chorionic gonadotropin (hCG), an exogenous LH-like stimulus, elicited an increase in circulating estradiol in the anestrous ewe (Fig.…”

Mathematical Studies of the Human Menstrual Cycle. I. Formulation of a Mathematical Model1

“…This morphological process occurs in stages with FSH and LH involved in varying ways (24)(25)(26)(27)(28). The steroid hormones are also important factors promoting these changes (8,24).…”